Coordinated wireless access protocol

ABSTRACT

An electronic device may coordinate access to a shared communication channel with one or more other electronic devices. After receiving frames from the one or more other electronic devices with information specifying back-off values associated with at least an access category for the one or more other electronic devices in a subsequent potential slot transmission opportunity, the electronic device may update a stored list of known occupied back-off values for the subsequent potential slot transmission opportunity. Then, the electronic device may select and may transmit to the one or more other electronic devices an available back-off value for the electronic device in the subsequent potential slot transmission opportunity that is not included in the stored list and that is associated with an access category. Next, during a slot corresponding to the selected back-off value, the electronic device may transmit a second frame to at least another electronic device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 62/393,289, entitled “COORDINATED WIRELESS ACCESSPROTOCOL” filed Sep. 12, 2016, the content of which is incorporated byreference herein in its entirety for all purposes.

FIELD

The described embodiments relate, generally, to wireless communicationsamong electronic devices in a wireless local area network (WLAN),including electronic devices and access points, and techniques forcontrolling channel access by synchronizing back-off values among theaccess points and/or the electronic devices in the WLAN.

BACKGROUND

Many wireless local area networks (WLANs), such as those based on acommunication protocol that is compatible with an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard (which issometimes referred to as ‘Wi-Fi’), involve contention-based distributedaccess systems. In particular, the WLANs are usually contention basedbecause they typically utilize unlicensed frequency bands or spectra,which are unpredictable and are often subject to interference.

For example, Wi-Fi access is often based on carrier sense multipleaccess (CSMA) with a collision avoidance technique, such as single-usertransmission via enhanced distributed channel access (EDCA). EDCAusually involves random access to the shared communication channel ormedium by contending electronic devices (which are sometimes referred toas ‘stations’ or STAs). In particular, as shown in FIG. 1, whichpresents an existing collision avoidance technique, air accessparameters (the arbitration interframe spacing number or AIFSN, theminimum and maximum contention window or CW, etc.) are usually specifiedby an access point in a WLAN. Moreover, an electronic device in the WLANis usually only allowed to transmit once a physical channel clearassessment (CCA) and a virtual CCA or carrier-sensing technique (such asthe network allocation vector or NAV) are both clear. Typically, theelectronic device selects a random back-off value N between 0 and theCW. Furthermore, the back-off time in the electronic device usuallyexpires only when the communication medium is idle for a time durationgreater than the AIFS plus N slots. However, if the back-off timers intwo electronic devices reach a back-off value of zero concurrently, atransmit collision occurs, and the CW is typically doubled. Therefore,in the event of a transmit collision, both of the electronic devices canbe penalized.

Consequently, the reliability of EDCA typically depends on the number ofelectronic devices contending for the communication medium. Inparticular, when there are four or more electronic devices concurrentlycontending to transmit on the communication channels, EDCA usuallyresults in a high rate of collisions (e.g., above 30%). Therefore, Wi-Fibased on EDCA may not suitable for use with medium-bandwidth orhigh-bandwidth applications (e.g., video streaming, mirroring, gaming,etc.) in dense communication channels.

The unpredictability of the interference with EDCA can make coordinationacross multiple electronic devices challenging (especially for anunmanaged WLAN), and, as described above, can result in the failure of acollision free period (CFP). In order to address these challenges,contention-free multi-user transmission in uplink has recently beenproposed in the IEEE 802.11ax standard. This approach can dramaticallychange how an electronic device accesses the communication medium. Inparticular, an electronic device can transmit without contending for thecommunication medium. Instead, an access point may contend for thecommunication medium on behalf of the electronic device, and may granttransmission opportunities to the electronic device using a triggerframe (which is sometimes referred to as ‘trigger-based access’ or‘trigger-based channel access,’ e.g., uplink multi-user transmission).During trigger-based uplink channel access, an access point may sensethe communication medium and, as needed, perform a back-off procedure onbehalf of potential uplink trigger-access-enabled electronic devices.Then, the access point may send a trigger frame with multi-userallocation information to the electronic devices. In response to thetrigger frame, the electronic devices may send uplink traffic in theallocated-resource units in a synchronized manner in a multi-usertransmission.

In principle, the use of trigger-based access and multi-usertransmission can significantly reduce the contention by the electronicdevices in the WLAN. Consequently, trigger-based access is oftenexpected to result in improved communication performance.

However, trigger-based access and multi-user transmission is notbackwards compatible with existing electronic devices, and may not besuitable for use with point-to-point ad-hoc links, such as Apple DirectWireless Link or AWDL (from Apple Inc. of Cupertino, Calif.),Neighborhood Area Network (NAN), and/or Wi-Fi Direct.

Alternative approaches to trigger-based access include the use of adynamic channel selection technique to select a ‘quiet’ communicationchannel to avoid collisions. However, the dynamic channel selectiontechnique is typically not an option when there are too fewcommunication channels, such as in the 2.4 GHz frequency band. Moreover,this approach typically adds channel synchronization overhead, whichusually consumes bandwidth and increases latency. Furthermore, thedynamic channel selection technique is also not backwards compatiblewith existing or legacy electronic devices.

SUMMARY

Embodiments relating to an electronic device that coordinates access toa shared communication channel using collision avoidance are described.During operation, an interface circuit in the electronic device mayreceive, from one or more other electronic devices in a set ofelectronic devices in a WLAN, one or more frames that includeinformation specifying one or more back-off values associated with atleast an access category for the one or more other electronic devices ina subsequent potential slot transmission opportunity. A given frame caninclude one or more back-off values associated with one or more accesscategories for a given other electronic device. In response, theinterface circuit may update a stored list of known occupied back-offvalues for the subsequent potential slot transmission opportunity.Moreover, the interface circuit may select an available back-off valuefor the electronic device in the subsequent potential slot transmissionopportunity that is not included in the stored list and that isassociated with an access category. Then, the interface circuit maytransmit, to the one or more other electronic devices, a frame thatincludes additional information specifying the selected back-off value.Next, the interface circuit may transmit, during a slot corresponding tothe selected back-off value, a second frame to at least one of the oneor more other electronic devices.

Note that a collision rate in the WLAN may be generally independent of anumber of electronic devices accessing the shared communication channelin the WLAN. In addition, a given one of the electronic device and theone or more other electronic devices may have a uniform accessprobability to the shared communication channel over a contention windowassociated with the subsequent potential slot transmission opportunity.Consequently, the throughput and latency may be improved relative toEDCA as the number of electronic devices increases.

Moreover, the back-off value may be randomly selected from availableback-off values not included in the stored list.

Furthermore, when a collision occurs between a selected back-off valueand an occupied back-off value in the list of known occupied back-offvalues, the interface circuit may select, for the electronic device,another available back-off value in the subsequent potential slottransmission opportunity that is not included in the stored list andthat is associated with an access category.

Additionally, the interface circuit may transmit and receive additionalframes from a legacy electronic device that uses EDCA instead of thepresently described collision avoidance techniques. Thus, the interfacecircuit may be compatible with an IEEE 802.11 standard that includesEDCA.

In some embodiments, the interface circuit updates the stored list ofknown occupied back-off values after each of the frames is received.

Note that the interface circuit may specify use of the collisionavoidance technique in a frame control field in the frame that specifiesthe selected back-off value and/or in the second frame that occupies theslot corresponding to the selected back-off value. In addition, theinterface circuit may include the additional information that specifiesthe selected back-off value in a quality-of-service (QoS) control fieldin a media access control (MAC) header in the second frame.

Other embodiments provide an interface circuit in the electronic device.

Still other embodiments provide a computer-program product for use withthe interface circuit in the electronic device. This computer-programproduct includes instructions for at least some of the aforementionedoperations performed by the interface circuit in the electronic device.

Still other embodiments provide a method for synchronizing back-offvalues. The method includes at least some of the aforementionedoperations performed by the interface circuit in the electronic device.

This Summary is provided for purposes of illustrating some exemplaryembodiments, so as to provide a basic understanding of some aspects ofthe subject matter described herein. Accordingly, it will be appreciatedthat the above-described features are only examples and should not beconstrued to narrow the scope or spirit of the subject matter describedherein in any way. Other features, aspects, and advantages of thesubject matter described herein will become apparent from the followingDetailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The included drawings are for illustrative purposes and serve only toprovide examples of possible structures and arrangements for thedisclosed systems and techniques for intelligently and efficientlymanaging communication between multiple associated user devices. Thesedrawings in no way limit any changes in form and detail that may be madeto the embodiments by one skilled in the art without departing from thespirit and scope of the embodiments. The embodiments will be readilyunderstood by the following detailed description in conjunction with theaccompanying drawings, wherein like reference numerals designate likestructural elements.

FIG. 1 is a drawing illustrating an existing collision avoidancetechnique.

FIG. 2 is a block diagram illustrating an example of electronic devicescommunicating wirelessly.

FIG. 3 is a flow diagram illustrating an example of a method forsynchronizing one or more back-off values using one of the electronicdevices in FIG. 1.

FIG. 4 is a flow diagram illustrating an example of communicationbetween electronic devices, such as electronic devices in FIG. 1.

FIG. 5 is a timing diagram illustrating an example of channel access byelectronic devices in FIG. 1 in different slots.

FIG. 6 is a drawing illustrating an example frame for use duringcommunication among at least some of the electronic devices in FIG. 1.

FIG. 7 is a block diagram illustrating an example electronic device,such as one of the electronic devices of FIG. 1.

Table 1 provides a comparison of an example of the performance of EDCAand a Coordinated Wireless Access Protocol.

Table 2 provides a comparison of an example of the performance of EDCAand a Coordinated Wireless Access Protocol in a mixed environment.

Note that like reference numerals refer to corresponding partsthroughout the drawings. Moreover, multiple instances of the same partare designated by a common prefix separated from an instance number by adash.

DETAILED DESCRIPTION

An electronic device may synchronize access to a shared communicationchannel with one or more other electronic devices. The electronic devicemay receive frames from the one or more other electronic devices withinformation specifying back-off values associated with at least anaccess category for the one or more other electronic devices, theback-off values corresponding to a subsequent potential slottransmission opportunity. Based on the information, the electronicdevice may update a stored list of known occupied back-off values forthe subsequent potential slot transmission opportunity. Then, theelectronic device may select an available back-off value for theelectronic device in the subsequent potential slot transmissionopportunity that is not included in the stored list and that isassociated with an access category. Next, the electronic device maytransmit, to the one or more other electronic devices, a frame thatincludes information specifying the selected back-off value.Furthermore, during a slot corresponding to the selected back-off value,the electronic device may transmit a second frame to at least anotherelectronic device.

By synchronizing the back-off values associated with at least the accesscategory in the subsequent potential slot transmission opportunity, thecontention avoidance technique may significantly reduce collisions in aWLAN when the electronic device and the one or more other electronicdevices attempt to access a shared communication channel. Consequently,a collision rate in the WLAN that includes the electronic device and theone or more other electronic devices may be generally independent of thenumber of electronic devices accessing the shared communication channelin the WLAN (i.e., with CWAP there is no longer a strong correlationbetween collisions and congestion, such that the collision rate isreduced relative to conventional contention avoidance techniques).Moreover, a given one of the electronic device and the one or more otherelectronic devices may have a uniform access probability to the sharedcommunication channel over a contention window associated with thesubsequent potential slot transmission opportunity. Therefore, thethroughput and latency (and, more generally, the communicationperformance) in the WLAN may be improved relative to EDCA as the numberof electronic devices increases. In addition, the contention avoidancetechnique(s) may ensure reduced access overhead, flexibility, and/or maybe backwards compatible with existing or legacy electronic devices thatdo not use the contention avoidance technique(s) (such as legacyelectronic devices that use EDCA). In the process, the contentionavoidance technique(s) may improve the user experience when using theelectronic device, and thus may increase customer satisfaction.

The contention avoidance technique(s) may be used during wirelesscommunication between electronic devices in accordance with acommunication protocol, such as an IEEE 802.11 standard (which issometimes referred to as Wi-Fi). The contention avoidance technique(s)may also be used with a wide variety of other communication protocols,and in access points and electronic devices (such as portable electronicdevices or mobile devices) that can incorporate multiple different radioaccess technologies (RATs) to provide connections through differentwireless networks that offer different services and/or capabilities.

An electronic device can include hardware and/or software to support awireless personal area network (WPAN) according to a WPAN communicationprotocol, such as those standardized by the Bluetooth® Special InterestGroup (in Kirkland, Wash.) and/or those developed by Apple Inc. (inCupertino, Calif.) that are referred to as AWDL. Moreover, theelectronic device can communicate via: a wireless wide area network(WWAN), a wireless metro area network (WMAN) a WLAN, near-fieldcommunication (NFC), a cellular-telephone or data network (such as usinga third generation (3G) communication protocol, a fourth generation (4G)communication protocol, e.g., Long Term Evolution or LTE, LTE Advanced(LTE-A), a fifth generation (5G) communication protocol, or otherpresent or future developed advanced cellular communication protocol)and/or another communication protocol. In some embodiments, thecommunication protocol includes a peer-to-peer communication technique.

The electronic device, in some embodiments, can also operate as part ofa wireless communication system, which can include a set of clientdevices, which can also be referred to as stations (STAs), clientelectronic devices, or client electronic devices, interconnected to anaccess point, e.g., as part of a WLAN, and/or to each other, e.g., aspart of a WPAN and/or an ‘ad hoc’ wireless network, such as a Wi-Fidirect connection. In some embodiments, the client device can be anyelectronic device that is capable of communicating via a WLANtechnology, e.g., in accordance with a WLAN communication protocol.Furthermore, in some embodiments, the WLAN technology can include aWi-Fi (or more generically a WLAN) wireless communication subsystem orradio, and the Wi-Fi radio can implement an IEEE 802.11 technology, suchas one or more of: IEEE 802.11a; IEEE 802.11b; IEEE 802.11g; IEEE802.11-2007; IEEE 802.11n; IEEE 802.11-2012; IEEE 802.11ac; IEEE802.11ax, or other present or future developed IEEE 802.11 technologies.

In some embodiments, the electronic device can act as a communicationshub that provides access to a WLAN and/or to a WWAN and, thus, to a widevariety of services that can be supported by various applicationsexecuting on the electronic device. Thus, the electronic device mayinclude an ‘access point’ that communicates wirelessly with otherelectronic devices (such as using Wi-Fi), and that provides access toanother network (such as the Internet) via IEEE 802.3 (which issometimes referred to as ‘Ethernet’).

Additionally, it should be understood that the electronic devicesdescribed herein may be configured as multi-mode wireless communicationdevices that are also capable of communicating via, e.g., different 3Gand/or second generation (2G) RATs. In these scenarios, a multi-modeelectronic device or user equipment (UE) can be configured to preferattachment to LTE networks offering faster data rate throughput, ascompared to other 3G legacy networks offering lower data ratethroughputs. For example, in some implementations, a multi-modeelectronic device is configured to fall back to a 3G legacy network,e.g., an Evolved High Speed Packet Access (HSPA+) network or a CodeDivision Multiple Access (CDMA) 2000 Evolution-Data Only (EV-DO)network, when LTE and LTE-A networks are otherwise unavailable.

In accordance with various embodiments described herein, the terms‘wireless communication device,’ ‘electronic device,’ ‘mobile device,’‘mobile station,’ ‘wireless station,’ ‘wireless access point,’‘station,’ ‘access point’ and ‘user equipment’ (UE) may be used hereinto describe one or more consumer electronic devices that may be capableof performing procedures associated with various embodiments of thedisclosure.

We now describe the contention avoidance techniques. FIG. 2 presents ablock diagram illustrating an example of electronic devicescommunicating wirelessly. One or more electronic devices 210 (such asone or more smartphones, laptop computers, notebook computers, tablets,wearable devices, or other such electronic device(s)) and access point212 may communicate wirelessly in a WLAN using an IEEE 802.11communication protocol. Thus, electronic devices 210 may be associatedwith access point 212. For example, electronic devices 210 and accesspoint 212 may wirelessly communicate while: detecting one another byscanning wireless channels, transmitting and receiving beacons or beaconframes on wireless channels, establishing connections (for example, bytransmitting connect requests), and/or transmitting and receivingpackets or frames (which may include a request and/or additionalinformation, such as data, as payloads). Note that access point 212 mayprovide access to a network, such as the Internet, (e.g., via anEthernet protocol) and may be a physical access point or a virtual or‘software’ access point that is implemented on a computer or anelectronic device.

As described further below with reference to FIG. 7, electronic devices210 and access point 212 may include subsystems, including any or all ofa networking subsystem, a memory subsystem, and a processor subsystem.In addition, electronic devices 210 and access point 212 may includeradios 214, e.g., in the networking subsystems. More generally,electronic devices 210 and access point 212 can be implemented as (orcan be included within) any electronic devices with networkingsubsystems that enable electronic devices 210 and access point 212 towirelessly communicate with one or more other electronic devices. Thiscan include transmitting beacons on wireless channels to enable theelectronic devices to make initial contact with or to detect each other,followed by exchanging subsequent data/management frames (such asconnect requests) to establish a connection, configure security options(e.g., IPSec), transmit and receive packets or frames via theconnection, etc.

As can be seen in FIG. 2, wireless signals 216 are communicated byradios 214-1 and 214-2 in electronic device 210-1 and access point 212,respectively. More generally, one or more of electronic devices 210and/or access point 212 may exchange frames using a Wi-Fi communicationprotocol in a WLAN. As described further below with reference to FIGS. 3and 4, one or more of electronic devices 210 (which are sometimesreferred to as a ‘set of electronic devices’) may transmit one or moreframes to other electronic devices 210 and/or access point 212 withinformation specifying back-off times associated with one or more accesscategories (such as video, voice, best effort and background data). Forexample, access point 212, electronic devices 210-2 and/or electronicdevice 210-3 may broadcast or advertise their back-off values for one ormore access categories in a subsequent potential slot transmissionopportunity. After receiving frames with the information, electronicdevice 210-1 may update a stored list of known occupied back-off valuesfor the subsequent potential slot transmission opportunity.

Then, electronic device 210-1 may select an available back-off value foritself in the subsequent potential slot transmission opportunity that isnot included in the stored list and that is associated with an accesscategory. Moreover, electronic device 210-1 may transmit, to any/all ofaccess point 212 and electronic devices 210-2 and/or 210-3, a frame thatincludes additional information specifying the selected back-off value.For example, electronic device 210-1 may broadcast or advertise theadditional information.

Next, electronic device 210-1 may transmit, during a slot correspondingto the selected back-off value (which may be the same as or differentfrom the subsequent potential slot transmission opportunity), a secondframe to at least one of access point 212, electronic device 210-2, andelectronic device 210-3.

By synchronizing the back-off values among access point 212 and any/allof electronic devices 210, this collision avoidance technique maysignificantly reduce collisions during contention for a sharedcommunication channel in the WLAN. Notably, the collision rate in theWLAN may be generally independent of a number of electronic devicesaccessing the shared communication channel in the WLAN (e.g., the set ofelectronic devices). Moreover, using CWAP, a given one of access point212, electronic device 210-1, electronic devices 210-2 and electronicdevice 210-3 may have a uniform access probability to the sharedcommunication channel over a contention window associated with thesubsequent potential slot transmission opportunity (i.e., CWAP mayensure fairness among electronic devices 210). Therefore, as describedbelow with reference to Tables 1 and 2, the throughput and latencyduring the communication may be improved relative to EDCA as the numberof electronic devices increases.

In addition, the contention avoidance technique may be backwardscompatible with existing or legacy electronic devices. Therefore,electronic device 210-1 may be compatible with an IEEE 802.11 standardthat includes EDCA. In some embodiments, electronic device 210-1supports EDCA.

In these ways, the contention avoidance technique may allow electronicdevices 210 and access point 212 to reduce contention in the WLAN and toimprove communication performance. These capabilities may improve theuser experience when using electronic devices, such as electronicdevices 210. For example, the contention avoidance technique(s) mayimprove the performance of medium/high-bandwidth applications (such asvideo streaming, mirroring, gaming) in dense communication channels orenvironments.

In the described embodiments, processing a packet or frame in one ofelectronic devices 210 and access point 212 includes: receiving wirelesssignals 216 encoding a packet or a frame; decoding/extracting the packetor frame from received wireless signals 216 to acquire the packet orframe; and processing the packet or frame to determine informationcontained in the packet or frame (such as data in the payload).

In general, communication via the WLAN in the contention avoidancetechnique may be characterized by a variety of communication-performancemetrics. For example, the communication-performance metrics may includeany/all of: a received signal strength (RSS), a data rate, a data ratefor successful communication (which is sometimes referred to as a‘throughput’), a latency, an error rate (such as a retry or resendrate), a mean-squared error of equalized signals relative to anequalization target, inter-symbol interference, multipath interference,a signal-to-noise ratio (SNR), a width of an eye pattern, a ratio of anumber of bytes successfully communicated during a time interval (suchas 1-10 s) to an estimated maximum number of bytes that can becommunicated in the time interval (the latter of which is sometimesreferred to as the ‘capacity’ of a communication channel or link),and/or a ratio of an actual data rate to an estimated data rate (whichis sometimes referred to as ‘utilization’).

Although we describe the network environment shown in FIG. 2 as anexample, in alternative embodiments, different numbers and/or types ofelectronic devices may be present. For example, some embodiments mayinclude more, fewer, and/or different electronic devices. As anotherexample, in other embodiments, different electronic devices can betransmitting and/or receiving packets or frames.

FIG. 3 presents a flow diagram illustrating an example method 300 forcoordinating synchronizing back-off values. This method may be performedby an electronic device, such as an interface circuit in access point212 or one of electronic devices 210 in FIG. 1. During operation, theelectronic device may receive, from one or more other electronic devicesin a set of electronic devices in a WLAN, one or more frames thatinclude information specifying one or more back-off values (operation310) associated with at least an access category for the one or moreother electronic devices in a subsequent potential slot transmissionopportunity. Note that a given frame may include one or more back-offvalues associated with one or more access categories for a given otherelectronic device.

In response, the electronic device may generate or update a stored listof known occupied back-off values (operation 312) for the subsequentpotential slot transmission opportunity. In some embodiments, theelectronic device updates the stored list of known occupied back-offvalues after each of the frames is received.

Further, the electronic device may select an available back-off value(operation 314) for the electronic device in the subsequent potentialslot transmission opportunity that is not included in the stored listand that is associated with an access category. For example, theback-off value may be randomly selected from available back-off valuesnot included in the stored list. In some embodiments, the back-off valueis selected using a random number generator that fairly and bounded intime selects a random number from a set of numbers that is not a powerof two. Then, the electronic device may transmit, to the one or moreother electronic devices, a frame that includes additional informationspecifying the selected back-off value (operation 316).

Next, the electronic device may transmit, during a slot corresponding tothe selected back-off value (which may be the same as or different fromthe subsequent potential slot transmission opportunity), a second frame(operation 318) to at least one of the one or more other electronicdevices.

In some embodiments, the electronic device optionally performs one ormore additional operations (operation 320). For example, the electronicdevice may transmit and receive additional frames from a legacyelectronic device that uses EDCA for accessing the wireless mediuminstead of the presently described collision avoidance technique(s).Thus, the interface circuit may be compatible with an IEEE 802.11standard that includes EDCA. Additionally, when a collision occursbetween a selected back-off value and an occupied back-off value in thelist of known occupied back-off values, the interface circuit may selectanother back-off value for the electronic device in the subsequentpotential slot transmission opportunity that is not included in thestored list and that is associated with an access category.

Moreover, there may be additional, fewer, or different operations inmethod 300. Furthermore, the order of the operations may be changed,and/or two or more operations may be combined into a single operation.

In some embodiments, at least some of the operations in method 300 areperformed by an interface circuit in the access point or the electronicdevice. For example, at least some of the operations may be performed byfirmware executed by an interface circuit, such as firmware associatedwith a MAC layer, as well as one or more circuits in a physical layer inthe interface circuit.

The contention avoidance technique is further illustrated in FIG. 4,which presents a flow diagram illustrating an example of communication,e.g., between electronic devices 210. Interface circuits 410-2 and 410-3in electronic devices 210-2 and 210-3 may transmit one or more frames412 that include information specifying one or more back-off values 414.

After receiving frames 412, interface circuit 410-1 in electronic device210-1 may update 416 a list 418 of known occupied back-off values inmemory 420 (such as a register). Note that memory 420 may separate fromor included in interface circuit 410-1.

Moreover, interface circuit 410-1 may select an available back-off value422 that is not included in the stored list and that is associated withan access category. Then, interface circuit 410-1 may transmit, to theone or more other electronic devices, frame(s) 424 including additionalinformation specifying the selected back-off value 422.

Next, interface circuit 410-1 may transmit, during a slot correspondingto the selected back-off value 422 (which may be the same as ordifferent from the subsequent potential slot transmission opportunity),a frame 426 to at least one of electronic devices 210-2 and 210-3, suchas electronic device 210-2.

Representative Embodiments

We now describe contention avoidance technique embodiments. Incontention-based channel-access techniques (such as EDCA), each of theelectronic devices in the WLAN independently contends for thecommunication channel. However, as the number of electronic devices inthe WLAN increases (and as the congestion increases), the probability ofa collision during channel access increases exponentially.

These challenges may be addressed by the proposed contention avoidancetechnique, which is sometimes referred to as Coordinated Wi-Fi AccessProtocol (CWAP). CWAP may be interoperable with legacy networks atlegacy performance. Moreover, the channel access opportunity in CWAP mayhave a uniform distribution, i.e., it may be ‘fairly’ distributedbetween the CWAP electronic devices. Consequently, a given CWAPelectronic device may be have an equal chance to access thecommunication channel over the contention window as the other electronicdevices.

In congested communication channels, CWAP may significantly improve thechannel aggregated throughput and average latency when compared to thelegacy Wi-Fi access techniques, such as EDCA. As noted previously, thiscapability may enable the use of bandwidth/latency sensitive stand-aloneor multi-users applications.

CWAP may enhance the legacy Wi-Fi access techniques by synchronizing thecommunication-channel access of the electronic devices that arecontending on the same communication channel, thereby resulting in areduced collision ratio.

During operation, an electronic device implementing CWAP (which issometimes referred to as a ‘CWAP electronic device’) may manage (ormaintain) a residual back-off table indicating, per access category, theknown occupied back-off values of electronic devices in the WLAN. Insome implementations, the residual back-off values in the residualback-off table may be updated in conjunction with the back-off value ofthe local electronic device (per access category). Moreover, a CWAPelectronic device may advertise, through packet transmission, the nextback-off count or value to use for this access category. Note that theadvertised back-off value may be selected by randomly drawing a back-offvalue from the non-occupied back-off values (e.g., those back-off valuesthat do not appear in the residual back-off table).

Furthermore, a new occupied back-off value (the advertised value) may beadded to the residual back-off table (per access category) after apacket or frame specifying a value is received on the communicationchannel. Additionally, a local back-off value of the CWAP electronicdevice may be updated after a frame is received from another CWAPelectronic device and/or in the event the local residual back-off valuecollides with an occupied back-off value as appearing in the residualback off table.

FIG. 5 presents an exemplary timing diagram illustrating channel accessby the electronic devices of FIG. 1 in different slots. Station (STA) 1may transmit a frame and receive an acknowledgement during a transmitopportunity 510-1, where transmission of the frame and receipt of theacknowledgement are indicated together by the block labeled Tx for STA1. After AIFS 512, there may be sixteen possible back-off values. Ofthese, sixteen back-off values, the particular values 1, 3, 6 and B (or11 in hexadecimal) may be occupied. STA 1 may select one of theavailable, free or unoccupied back-off values (denoted by the letter F),where the selected back-off value 514 is denoted by S and has a back-offvalue of 4.

In the next transmit opportunity 510-2, STA 2 may have the lowestback-off value (such as a back-off value 1). Therefore, STA 2 maytransmit a frame and receive an acknowledgment. After AIFS 512, theremay be sixteen possible back-off values. Of these, sixteen back-offvalues, the particular values 2, 3, 5 and A (or 10 in hexadecimal) maybe occupied (note that the back-off values decremented when the back-offvalue for STA 1 was removed from the back-off value table, and thus theprevious back-off values of 3, 6, and B became the current back-offvalues of 2, 5, and A, while the previously selected back-off value of 4became the current back-off value of 3). STA 2 may select one of theavailable, free or unoccupied back-off values (F), where the selectedback-off value 516 is denoted by S and has the back-off value of 7.

Furthermore, in the following transmit opportunity 510-3, STA 3 may havethe lowest back-off value (such as a back-off value 2). Therefore, STA 3may transmit a frame and receive an acknowledgment. After AIFS 512,there may be sixteen possible back-off values. Of these, sixteenback-off values, the particular values 2, 4, 6 and 9 may be occupied(note that the back-off values decremented by one when the back-offvalue for STA 2 was removed from the back-off value table, and thus theprevious back-off values of 3, 5, and A became the current back-offvalues of 2, 4 and 9, while the previously selected back-off value of 7became the current back-off value of 6). STA 3 may select one of theavailable, free or unoccupied back-off values (F), denoted by S, wherethe selected back-off value 518 is denoted by S and has the back-offvalue of 8.

As shown in FIG. 6, which presents a drawing illustrating a frame 600for use during communication among at least some of the electronicdevices illustrated in FIG. 1. This frame may be formatted to includethe following fields (or elements): frame control (FC) 610, duration612, address 1 614, address 2 616, address 3 618, sequence control 620,address 4 622, QoS control 624, high-throughput (HT) control 626, framebody 628, and/or frame check sequence (FCS) 630. Moreover, QoS control624 may include the following sub-fields (or sub-elements): trafficidentifier (TID) 632, a field with a value of ‘0’ 634, an acknowledgment(ACK) policy 636, an indicator of whether an aggregated MAC service dataunit is present 638, and/or a selected back-off value 640. Note thatCWAP operation may be indicated by setting the protocol version in framecontrol 610 to a specific value, such as the value ‘10’, (where legacyelectronic devices may use the value ‘00’). Moreover, the selectedback-off value 638 may be contained in bits 8-15 of the QoS controlfield 624 of the MAC header (as the QoS control field 624 is an unusedfield in the EDCA specification). In other implementations, frame 600can include different, more, or fewer fields, and the respective sizesof any/all fields can vary. Moreover, one or more values used for a CWAPtechnique can be implemented using one or more different fields ordifferent bits of a particular field than the example shown.

Table 1 provides a comparison of the performance of EDCA and CWAP with aminimum contention window of 15, N electronic devices, User DatagramProtocol (UDP) transmission, and a maximum UDP throughput at a 54 Mbpsphysical data rate. The throughput (TP) decreases and the collision rate(CR) increases as the number of electronic devices in the WLANincreases. In contrast, the throughput decreases less and the collisionrate is essentially unchanged using CWAP. Moreover, Table 2 provides acomparison of the performance of EDCA and CWAP with N legacy and CWAPelectronic devices (e.g., a mixed environment) and a maximum UDPthroughput at a 54 Mbps physical data rate. Once again, the CWAPelectronic devices have improved throughput relative to the legacyelectronic devices.

TABLE 1 Number Legacy CWAP Legacy PHY of Legacy Legacy Average TP CWAPAverage Tx Rate Streaming TP CR Latency (Total CR Latency ΔTP Type(Mbps) Devices (Total TP) (%) (ms) TP) (%) (ms) (%) UDP 54 1 28.4 0 <128.4 0 <1 0 (28.4) (28.4) 2 14.3 11 <1 15.6 0 <1 0 (28.5) (31.3) 5 5.425 1  6.6 0 1 14 (27.7) (33)   10 2.6 36 4  3.3 0 3 27 (25.9) (33.2) 151.6 39 6  2.2 0 4 36 (24.9) (33.9) 20 1.2 43 8  1.7 1 7 39 (24.1) (33.5)30 0.8 48 14  1.1 2.5 10 45 (23.1) (33.5) 40 0.5 52 21  0.8 3 13 49(22.6) (33.7)

TABLE 2 Number Number of Legacy of CWAP Tx PHY Rate Streaming StreamingLegacy CWAP Total Type (MbPs) Devices Devices TP TP TP UDP 54 4 0 7.0 —28.0 1 3 3.8 8.9 30.9 0 4 — 7.8 31.1 10 0 2.6 — 25.9 5 5 1.6 4.4 29.0 19 <0.1 3.7 33.4 0 10 — 3.3 33.2

In summary, in some embodiments of the contention avoidance technique(s)described, the electronic devices coordinate their back-off values for asubsequent potential slot transmission opportunity to reduce oreliminate collisions when the electronic devices attempt to access theshared communication channel.

We now describe embodiments of an electronic device. FIG. 7 presents ablock diagram of an electronic device 700 (which may be an access point,another electronic device, such as a station or a legacy electronicdevice) in accordance with some embodiments. This electronic deviceincludes processing subsystem 710, memory subsystem 712, and networkingsubsystem 714. Processing subsystem 710 includes one or more devicesconfigured to perform computational operations. For example, processingsubsystem 710 can include one or more microprocessors,application-specific integrated circuits (ASICs), microcontrollers,programmable-logic devices, and/or one or more digital signal processors(DSPs).

Memory subsystem 712 includes one or more devices for storing dataand/or instructions for processing subsystem 710 and networkingsubsystem 714. For example, memory subsystem 712 can include dynamicrandom access memory (DRAM), static random access memory (SRAM), aread-only memory (ROM), flash memory, and/or other types of memory. Insome embodiments, instructions for processing subsystem 710 in memorysubsystem 712 include: one or more program modules or sets ofinstructions (such as program module 722 or operating system 724), whichmay be executed by processing subsystem 710. For example, a ROM canstore programs, utilities or processes to be executed in a non-volatilemanner, and DRAM can provide volatile data storage, and may storeinstructions related to the operation of electronic device 700. Notethat the one or more computer programs may constitute a computer-programmechanism, a computer-readable storage medium or software. Moreover,instructions in the various modules in memory subsystem 712 may beimplemented in: a high-level procedural language, an object-orientedprogramming language, and/or in an assembly or machine language.Furthermore, the programming language may be compiled or interpreted,e.g., configurable or configured (which may be used interchangeably inthis discussion), to be executed by processing subsystem 710. In someembodiments, the one or more computer programs are distributed over anetwork-coupled computer system so that the one or more computerprograms are stored and executed in a distributed manner.

In addition, memory subsystem 712 can include mechanisms for controllingaccess to the memory. In some embodiments, memory subsystem 712 includesa memory hierarchy that comprises one or more caches coupled to a memoryin electronic device 700. In some of these embodiments, one or more ofthe caches is located in processing subsystem 710.

In some embodiments, memory subsystem 712 is coupled to one or morehigh-capacity mass-storage devices (not shown). For example, memorysubsystem 712 can be coupled to a magnetic or optical drive, asolid-state drive, or another type of mass-storage device. In theseembodiments, memory subsystem 712 can be used by electronic device 700as fast-access storage for often-used data, while the mass-storagedevice is used to store less frequently used data.

Networking subsystem 714 includes one or more devices configured tocouple to and communicate on a wired and/or wireless network (i.e., toperform network operations), including: control logic 716, an interfacecircuit 718 and a set of antennas 720 (or antenna elements) in anadaptive array that can be selectively turned on and/or off by controllogic 716 to create a variety of optional antenna patterns or ‘beampatterns.’ (While FIG. 7 includes set of antennas 720, in someembodiments electronic device 700 includes one or more nodes, such asnodes 708, e.g., a pad, which can be coupled to set of antennas 720.Thus, electronic device 700 may or may not include set of antennas 720.)For example, networking subsystem 714 can include a Bluetooth™networking system, a cellular networking system (e.g., a 3G/4G/5Gnetwork such as UMTS, LTE, etc.), a universal serial bus (USB)networking system, a networking system based on the standards describedin IEEE 802.11 (e.g., a Wi-Fi® networking system), an Ethernetnetworking system, and/or another networking system.

Networking subsystem 714 includes processors, controllers,radios/antennas, sockets/plugs, and/or other devices used for couplingto, communicating on, and handling data and events for each supportednetworking system. Note that mechanisms used for coupling to,communicating on, and handling data and events on the network for eachnetwork system are sometimes collectively referred to as a ‘networkinterface’ for the network system. Moreover, in some embodiments a‘network’ or a ‘connection’ between the electronic devices does not yetexist. Therefore, electronic device 700 may use the mechanisms innetworking subsystem 714 for performing simple wireless communicationbetween the electronic devices, e.g., transmitting advertising or beaconframes and/or scanning for advertising frames transmitted by otherelectronic devices.

Within electronic device 700, processing subsystem 710, memory subsystem712, and networking subsystem 714 are coupled together using bus 728that facilitates data transfer between these components. Bus 728 mayinclude an electrical, optical, and/or electro-optical connection thatthe subsystems can use to communicate commands and data among oneanother. Although only one bus 728 is shown for clarity, differentembodiments can include a different number or configuration ofelectrical, optical, and/or electro-optical connections among thesubsystems.

In some embodiments, electronic device 700 includes a display subsystem726 for displaying information on a display, which may include a displaydriver and the display, such as a liquid-crystal display, a multi-touchtouchscreen, etc. Display subsystem 726 may be controlled by processingsubsystem 710 to display information to a user (e.g., informationrelating to incoming, outgoing, or an active communication session).

Electronic device 700 can also include a user-input subsystem 730 thatallows a user of the electronic device 700 to interact with electronicdevice 700. For example, user-input subsystem 730 can take a variety offorms, such as: a button, keypad, dial, touch screen, audio inputinterface, visual/image capture input interface, input in the form ofsensor data, etc.

Electronic device 700 can be (or can be included in) any electronicdevice with at least one network interface. For example, electronicdevice 700 may include: a cellular telephone or a smartphone, a tabletcomputer, a laptop computer, a notebook computer, a personal or desktopcomputer, a netbook computer, a media player device, an electronic bookdevice, a MiFi® device, a smartwatch, a wearable computing device, aportable computing device, a consumer-electronic device, an accesspoint, a router, a switch, communication equipment, test equipment, aswell as any other type of electronic computing device having wirelesscommunication capability that can include communication via one or morewireless communication protocols.

Although specific components are used to describe electronic device 700,in alternative embodiments, different components and/or subsystems maybe present in electronic device 700. For example, electronic device 700may include one or more additional processing subsystems, memorysubsystems, networking subsystems, and/or display subsystems.Additionally, one or more of the subsystems may not be present inelectronic device 700. Moreover, in some embodiments, electronic device700 may include one or more additional subsystems that are not shown inFIG. 7. Also, although separate subsystems are shown in FIG. 7, in someembodiments some or all of a given subsystem or component can beintegrated into one or more of the other subsystems or component(s) inelectronic device 700. For example, in some embodiments program module722 is included in operating system 724 and/or control logic 716 isincluded in interface circuit 718.

Moreover, the circuits and components in electronic device 700 may beimplemented using any combination of analog and/or digital circuitry,including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore,signals in these embodiments may include digital signals that haveapproximately discrete values and/or analog signals that have continuousvalues. Additionally, components and circuits may be single-ended ordifferential, and power supplies may be unipolar or bipolar.

An integrated circuit (which is sometimes referred to as a‘communication circuit’) may implement some or all of the functionalityof networking subsystem 714. This integrated circuit may includehardware and/or software mechanisms that are used for transmittingwireless signals from electronic device 700 and receiving signals atelectronic device 700 from other electronic devices. Aside from themechanisms herein described, radios are generally known in the art andhence are not described in detail. In general, networking subsystem 714and/or the integrated circuit can include any number of radios. Notethat the radios in multiple-radio embodiments function in a similar wayto the described single-radio embodiments.

In some embodiments, networking subsystem 714 and/or the integratedcircuit include a configuration mechanism (such as one or more hardwareand/or software mechanisms) that configures the radio(s) to transmitand/or receive on a given communication channel (e.g., a given carrierfrequency). For example, in some embodiments, the configurationmechanism can be used to switch the radio from monitoring and/ortransmitting on a given communication channel to monitoring and/ortransmitting on a different communication channel. (Note that‘monitoring’ as used herein comprises receiving signals from otherelectronic devices and possibly performing one or more processingoperations on the received signals)

In some embodiments, an output of a process for designing the integratedcircuit, or a portion of the integrated circuit, which includes one ormore of the circuits described herein may be a computer-readable mediumsuch as, for example, a magnetic tape or an optical or magnetic disk.The computer-readable medium may be encoded with data structures orother information describing circuitry that may be physicallyinstantiated as the integrated circuit or the portion of the integratedcircuit. Although various formats may be used for such encoding, thesedata structures are commonly written in: Caltech Intermediate Format(CIF), Calma GDS II Stream Format (GDSII) or Electronic DesignInterchange Format (EDIF). Those of skill in the art of integratedcircuit design can develop such data structures from schematic diagramsof the type detailed above and the corresponding descriptions and encodethe data structures on the computer-readable medium. Those of skill inthe art of integrated circuit fabrication can use such encoded data tofabricate integrated circuits that include one or more of the circuitsdescribed herein.

While the preceding discussion used a Wi-Fi communication protocol as anillustrative example, in other embodiments a wide variety ofcommunication protocols and, more generally, wireless contentionavoidance techniques may be used. Thus, the contention avoidancetechnique may be used in a variety of network interfaces. Furthermore,while some of the operations in the preceding embodiments wereimplemented in hardware or software, in general the operations in thepreceding embodiments can be implemented in a wide variety ofconfigurations and architectures. Therefore, some or all of theoperations in the preceding embodiments may be performed in hardware, insoftware or both. For example, at least some of the operations in thecontention avoidance technique may be implemented using program module722, operating system 724 (such as a driver for interface circuit 718)or in firmware in interface circuit 718. Alternatively or additionally,at least some of the operations in the contention avoidance techniquemay be implemented in a physical layer, such as hardware in interfacecircuit 718. In some embodiments, the contention avoidance technique isimplemented, at least in part, in a MAC layer and/or in a physical layerin interface circuit 718.

Furthermore, in general, the contention avoidance technique may be usedto facilitate scheduled channel access in time and/or frequency inconjunction with multi-user multiple input multiple output (MU-MIMO)and/or orthogonal frequency division multiple access (OFDMA).

In the preceding description, we refer to ‘some embodiments.’ Note that‘some embodiments’ describes a subset of all of the possibleembodiments, but does not always specify the same subset of embodiments.

The foregoing description is intended to enable any person skilled inthe art to make and use the disclosure, and is provided in the contextof a particular application and its requirements. Moreover, theforegoing descriptions of embodiments of the present disclosure havebeen presented for purposes of illustration and description only. Theyare not intended to be exhaustive or to limit the present disclosure tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art, and the generalprinciples defined herein may be applied to other embodiments andapplications without departing from the spirit and scope of the presentdisclosure. Additionally, the discussion of the preceding embodiments isnot intended to limit the present disclosure. Thus, the presentdisclosure is not intended to be limited to the embodiments shown, butis to be accorded the widest scope consistent with the principles andfeatures disclosed herein.

What is claimed is:
 1. An electronic device, comprising: one or morenodes configured to communicatively couple to an antenna; and aninterface circuit, communicatively coupled to the one or more nodes,configured to communicate with a set of electronic devices in a wirelesslocal area network (WLAN), and configured to: receive, from each of oneor more other electronic devices in the set of electronic devices, aframe comprising information specifying a back-off value for the otherelectronic device in a subsequent potential slot transmissionopportunity; update, in response to the information, a stored list ofknown occupied back-off values for the subsequent potential slottransmission opportunity; select an available back-off value for theelectronic device in the subsequent potential slot transmissionopportunity that is not included in the stored list; transmit, to theone or more other electronic devices, a frame that includes additionalinformation specifying the selected back-off value; and transmit, duringa slot corresponding to the selected back-off value, a second frame toat least another electronic device.
 2. The electronic device of claim 1,wherein a collision rate in the WLAN is reduced relative to enhanceddistributed channel access (EDCA) as a number of electronic devicesaccessing a shared communication channel in the WLAN increases.
 3. Theelectronic device of claim 2, wherein throughput and latency associatedwith communication with the one or more other electronic devices isimproved relative to EDCA as a number of electronic devices in the WLANincreases.
 4. The electronic device of claim 1, wherein a given one ofthe electronic device and the one or more other electronic devices mayhave a uniform access probability to a shared communication channel overa contention window associated with the subsequent potential slottransmission opportunity.
 5. The electronic device of claim 1, whereinthe back-off value is randomly selected from available back-off valuesnot included in the stored list.
 6. The electronic device of claim 1,wherein, when a collision occurs between a selected back-off value andan occupied back-off value in the list of known occupied back-offvalues, the interface circuit selects another available back-off valuefor the electronic device in the subsequent potential slot transmissionopportunity that is not included in the stored list and that isassociated with an access category.
 7. The electronic device of claim 1,wherein the interface circuit is compatible with an IEEE 802.11 standardthat includes enhanced distributed channel access (EDCA).
 8. Theelectronic device of claim 1, wherein the interface circuit isconfigured to update the stored list of known occupied back-off valuesafter each frame is received.
 9. The electronic device of claim 1,wherein the interface circuit is configured to specify an ability tosynchronize back-off values with the one or more other electronicdevices in a frame control field in the frame and/or the second frame.10. The electronic device of claim 1, wherein the interface circuit isconfigured to include the additional information that specifies theselected back-off value in a quality-of-service (QoS) control field in amedia access control (MAC) header in the second frame.
 11. Anon-transitory computer-readable storage medium storing instructionsthat, when executed by an interface circuit included in a communicationdevice, cause the communication device to synchronize one or moreback-off values, by carrying out one or more operations that comprise:receiving, from one or more other electronic devices in a set ofelectronic devices in a wireless local area network (WLAN), one or moreframes that include information specifying one or more back-off valuesassociated with at least an access category for the one or more otherelectronic devices in a subsequent potential slot transmissionopportunity, wherein a given frame includes one or more back-off valuesassociated with one or more access categories for a given otherelectronic device; updating, in response to the information, a storedlist of known occupied back-off values for the subsequent potential slottransmission opportunity after each of the one or more frames isreceived; selecting an available back-off value for the communicationdevice in the subsequent potential slot transmission opportunity that isnot included in the stored list and that is associated with an accesscategory; transmitting, to the one or more other electronic devices, aframe that includes additional information specifying the selectedback-off value; and transmitting, during a slot corresponding to theselected back-off value, a second frame to at least one of the one ormore other electronic device.
 12. The non-transitory computer-readablestorage medium of claim 11, wherein a collision rate in the WLAN isapproximately independent of a number of electronic devices accessing ashared communication channel in the WLAN.
 13. The non-transitorycomputer-readable storage medium of claim 12, wherein throughput andlatency associated with communication with the one or more otherelectronic devices is improved relative to enhanced distributed channelaccess (EDCA) as a number of electronic devices in the WLAN increases.14. The non-transitory computer-readable storage medium of claim 11,wherein the back-off value is randomly selected from available back-offvalues not included in the stored list.
 15. The non-transitorycomputer-readable storage medium of claim 11, wherein the interfacecircuit is compatible with an IEEE 802.11 standard that includesenhanced distributed channel access (EDCA).
 16. A method forcoordinating one or more back-off values, comprising: in an interfacecircuit in an electronic device: receiving, from one or more otherelectronic devices in a set of electronic devices in a wireless localarea network (WLAN), one or more frames that include informationspecifying one or more back-off values associated with at least anaccess category for the one or more other electronic devices in asubsequent potential slot transmission opportunity, wherein a givenframe includes one or more back-off values associated with one or moreaccess categories for a given other electronic device; updating, inresponse to the information, a stored list of known occupied back-offvalues for the subsequent potential slot transmission opportunity;selecting an available back-off value for the communication device inthe subsequent potential slot transmission opportunity that is notincluded in the stored list and that is associated with an accesscategory; transmitting, to the one or more other electronic devices, aframe that includes additional information specifying the selectedback-off value; and transmitting, during a slot corresponding to theselected back-off value, a second frame to at least one of the one ormore other electronic device.
 17. The method of claim 16, wherein acollision rate in the WLAN is approximately independent of a number ofelectronic devices accessing a shared communication channel in the WLAN.18. The method of claim 17, wherein throughput and latency associatedwith communication with the one or more other electronic devices isimproved relative to enhanced distributed channel access (EDCA) as anumber of electronic devices in the WLAN increases.
 19. The method ofclaim 16, wherein the additional information that specifies the selectedback-off value is included in a quality-of-service (QoS) control fieldin a media access control (MAC) header in the second frame.
 20. Themethod of claim 16, wherein the interface circuit is compatible with anIEEE 802.11 standard that includes enhanced distributed channel access(EDCA).